I am trying to replace an old recessed medicine cabinet. The size is off from any cabinet I can find. Its off by several inches, therefore will not fit in the hole in the wall. Any ideas on how to either fill in the gap so that a smaller cabinet will fit? There is also a box above that has the light attached to it. I am having a hard time finding a light that I can put over it without removing the box. The apartment is pre war and deeming very difficult to find updated items. Appreciate any advice. Thanks